If I remember correctly, part of the trail is still dirt. But, once you get to the dam, you'd take Alma Bridge Road, which runs right across the dam. Turn on Aldercroft Heights Rd, follow that to Old Santa Cruz Highway, then on to Summit.
Cribbed from my club's Academy route sheets:
Alma Bridge Rd
4.3 R Aldercroft HTS Rd
4.8 L Old Santa Cruz Hwy
6.2 Holy City Glass (good place for a break-even better if they are open!)
8.4 L Summit Rd
10.9 L Summit Store
Summit Rd and Old Santa Cruz can be spooky - they are narrow.